Extreme Max Single Post Horizontal Bunk Guide On System 18" Post. They'll help you load faster and safer keep you from loading too deep keep your trailer position true and are especially helpful at night. They will fit bunk or roller-style trailers up to 3" wide x 4.25" tall. 18" carpet-padded horizontal bunks sit on 96 angled vertical arms. These guide-ons can be adjusted horizontally up to 19" (3" trailer frame) or 21"" (2" trailer frame). Vertically adjustable from 19" to 25". Extreme Max Guide-Ons are zinc-coated and intended for freshwater use only. Use in saltwater or brackish water will corrode and deteriorate the finish. 7" bolt kit available for trailer frames up to 5.25" tall (Extreme Max 3005.4050)8" bolt kit available for trailer frames up to 6.25" tall (Extreme Max 3005.4053). Features of Extreme Max 3005.3837 Single Post Horizontal Bunk Guide On System 18" Post Includes a pair of carpet-padded boat trailer guide-ons perfect for 14' to 16' boats; Fits bunk or roller-style trailer frames up to 3" wide x 4.25" tall 18" carpet padded bunks are vertically adjustable from 19" to 25" and sit on 96 angled vertical arms with up to 19" (3" trailer frame) or 21" (2" trailer frame) of total horizontal adjustment Zinc-coated for freshwater corrosion-resistance not intended for use in saltwater or brackish water The size and shape of trailer frames can vary drastically please measure your boat on the trailer before ordering to ensure a proper fit Hardware to fit taller trailer frames (5.25" and 6.25") is available see long description Package Contents: Extreme Max 3005.3837 Single Post Horizontal Bunk Guide On System 18" Post Extreme Max 3005.3837: Single Post Horizontal Bunk Guide On System 18" Post